The emission of particulate matter in exhaust from compression-ignition engines is regulated for environmental reasons. Thus, vehicles equipped with compression-ignition engines often include after-treatment components such as particulate filters, catalyzed soot filters and adsorption catalysts for removing particulate matter and other regulated constituents (e.g., nitrogen oxides or NOx) from their exhaust streams. Particulate filters and other after-treatment components can be effective, but can also increase back pressure as they collect particulate matter.
Particulate matter may include ash and unburned carbon particles generally referred to as soot. As this carbon-based particulate matter accumulates in the after-treatment components, it can increase back pressure in the exhaust system. Engines that have large rates of particulate mass emission can develop excessive back pressure levels in a relatively short period of time, decreasing engine efficiency and power producing capacity. Therefore, it is desired to have particulate filtration systems that minimize back-pressure while effectively capturing particulate matter in the exhaust.
To accomplish both of these competing goals, after-treatment components must be regularly monitored and maintained either by replacing components or by removing the accumulated soot. Cleaning the accumulated soot from an after-treatment component can be achieved via oxidation to CO2 (i.e., burning-off) and is known in the art as regeneration. To avoid service interruptions, regeneration is generally preferred over replacement of after-treatment components.
An engine control system may use a soot model to deduce (i.e., predict) a mass of soot accumulated in the after-treatment component by monitoring properties of the exhaust stream as it flows through the after-treatment component. The control system can use the deduced soot mass data to monitor soot loading over time, to determine or anticipate when regeneration may be necessary or desirable, to facilitate a regeneration event, and/or to effectuate control over a regeneration process or other remedial measures. Soot models typically need to be accurate while accounting for a number of vehicle conditions.
To ensure that after-treatment components are in good operating order, performance monitoring for faults in the after-treatment components is also performed. High accuracy soot and sensor models can be used to determine when a fault condition exists in a particulate filter. Making fault comparisons between multiple models can increase a risk of incorrectly declaring that a fault exists, particularly when performing time-based comparisons. Incorrectly declaring that a fault exists may lead to performance of otherwise unnecessary diagnostic and maintenance operations.
Accordingly, it is desirable to provide systems and methods for monitoring particulate filter performance in an exhaust system that reduces the risk of incorrectly declaring a fault.